Are you using a PanelView Plus terminal ? Those terminals have several third-party communication drivers that support general-purpose protocols like Modbus/TCP.
Does your specific PNOZ relay have an Ethernet interface module ?
The PNOZ RS-232 serial protocol doesn't appear to be compatible with Modbus or any other protocol that the PanelView Plus supports. The "custom protocol" driver in the PanelView is not for novices.
This is the user manual I was reading from:
http://downloads.pilz.nl/downloads/PNOZMulti/PNOZmulti_Com_Interface_Op_Man_1001154-EN-10.pdf